Note: Descriptions are shown in the official language in which they were submitted.
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IMPROVED HEAT TRANSFER THROUGH ELECTRICAL SUBMERSIBLE PUMP
MOTOR
Field of the Invention
This invention relates in general to well pumps, and in particular to an
electrical submersible
pump motor using internal oil circulation to increase heat transfer.
Cross-Reference to Related Applications
This application claims priority to provisional application 61/165,339, filed
March 31, 2009.
Back2rround
Electrical submersible pumps ("ESP") can be used to pump fluid from a wellbore
towards the
surface of the earth. The ESP is inserted inside the wellbore, generally at
great depths below the
surface of the earth. The ESP includes a pump assembly, a motor, and a seal
section between the
pump and the motor. The motor includes a rotor that rotates within a stator.
The rotor rotates on
bearings which are connected to the stator. The bearings can generate a
significant amount of
heat that must be removed. Heat may also be generated by other heat sources,
such as, for
example, electrical resistance in the windings of the stator, rotor, and in
the laminations of the
motor. Failure to remove the heat can significantly shorten the life of the
motor.
To remove the heat, it is desirable to move the heat from the rotor and stator
to the motor
housing. The heat is then conducted through the motor housing to wellbore
fluid located outside
of the motor housing. There is a problem, however, in transferring the heat
from the stator to the
housing.
In a typical motor, there is a slight gap between the stator and the motor
housing. The gap is
necessary to be able to install and remove the stator from the housing.
Unfortunately, the gap is
generally filled with air, which is a poor heat conductor.
It is desirable to efficiently transfer heat from the stator to the motor
housing.
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Summary of the Invention
In this invention, internal grooves are used to facilitate lubricant flow
between the stator and the
motor housing in an electrical submersible pump ("ESP") motor. The lubricant
flow between the
stator and the housing increases the rate of heat transfer from the stator to
the housing, and
therefore increases the rate of heat transfer from the housing to production
fluid in contact with
the exterior of the housing.
In some embodiments, grooves are formed on the interior of the motor housing.
The grooves
may extend longitudinally past each end of the stator, from an oil reservoir
at one end of the
housing to an oil reservoir at the other end of the housing. In various
embodiments, the grooves
may be longitudinal, circumferential, or helical. Furthermore, a plurality of
groove types may be
used in a single embodiment. In some embodiments, grooves on the interior of
the housing
create a corresponding ridge on the exterior of the housing.
In some embodiments, grooves are formed on the exterior of the stator. The
grooves may extend
from one end of the stator to the other. Like the housing grooves, the stator
grooves may be
longitudinal, circumferential, or helical. A plurality of groove types may be
used. Stator
grooves may be used in the same embodiment as housing grooves.
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Brief Description of the Drawings
Figure 1 is a schematic view of a pump assembly in accordance with an
embodiment of the
invention in a wellbore.
Figure 2 is a sectional view of a motor housing of the motor in Figure l with
internal oil grooves.
Figure 3 is a cross-sectional view of the motor housing from Figure 2, taken
along the line 3-3 of
Figure 2 to illustrate longitudinal grooves.
Figure 4 is a cross-sectional view of an alternative embodiment of a motor
housing having
circumferential grooves.
Figure 5 is a cross-sectional view of another alternative embodiment of a
motor housing having
longitudinal and helical grooves.
Figure 6 is a sectional view of another alternative embodiment of a motor
housing with internal
longitudinal lubricant grooves and external ridges.
Figure 7 is a cross-sectional view of the motor housing of Figure 6, taken
along the line 7-7 of
Figure 6.
Figure 8 is a side-view of an embodiment of a stator having longitudinal
lubricant grooves.
Figure 9 is a side view of another embodiment of a stator having helical
lubricant grooves.
Figure 10 is a side view of another embodiment of a stator having
circumferential lubricant
grooves.
Figure 1 I is a sectional view of an embodiment of the pump assembly of Figure
1, having
dimples on the pump motor housing.
Figure 12 is an orthogonal view of another embodiment of the shroud of Figure
1, showing one
half of a two-part clamshell shroud with fins.
Figure 13 is a side view of an alternative embodiment of the pump of Figure 1,
having external
oil circulation tubes.
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Detailed Description
[00011 The present invention will now be described more fully hereinafter with
reference to the
accompanying drawings which illustrate embodiments of the invention. This
invention may,
however, be embodied in many different forms and should not be construed as
limited to the
illustrated embodiments set forth herein. Rather, these embodiments are
provided so that this
disclosure will be thorough and complete, and will fully convey the scope of
the invention to
those skilled in the art. Like numbers refer to like elements throughout, and
the prime notation, if
used, indicates similar elements in alternative embodiments.
[0002] Referring to Figure 1, wellbore casing 10 is shown in a vertical
orientation, but it could
be inclined. Pump 12 is suspended inside casing 10 and is used to pump
wellbore fluid up from
the well. Wellbore fluid may be any kind of fluid including, for example,
crude oil, water, gas,
liquids, other downhole fluids, or fluids such as water that may be injected
into a rock formation
for secondary recovery operations. Indeed, wellbore fluid can include desired
fluids produced
from a well or by-product fluids that an operator desires to remove from a
well. Pump 12 may
be centrifugal or any other type of pump and may have an oil-water separator
or a gas separator.
Pump 12 is driven by a shaft 14, operably connected to a motor 16. Seal
section 18 is mounted
between the motor 16 and pump 12. The seal section reduces a pressure
differential between
lubricant in the motor and well fluid. Motor 16 comprises housing 20. Housing
20 can be a
cylindrical housing, and typically encases the other components of motor 16.
Preferably, the
fluid produced by the well ("production fluid") flows past motor 16, enters an
intake 22 of pump
12, and is pumped up through tubing 24. Normally, motor 16 is located below
the pump 12 in
the wellbore. The production fluid may enter the pump 12 at a point above the
motor 16, such
that the fluid is drawn up, past the motor housing 20 of the motor 16, and
into the pump inlet 22.
[0003] Stator 30 is stationarily mounted in housing 20. Stator 30 comprises a
large number of
stator disks (laminations) having slots through them which are interlaced with
three-phase copper
windings. Stator 30 has an axial passage that extends through it. The
clearance between the OD
of stator 30 and ID of the housing 20 may be quite small.
[00041 Rotor 32 is located within the stator 30 passage and is rotably mounted
on a plurality of
bearings, the bearings being located between the rotor and the stator. Rotor
32 is mounted to
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shaft 14. Motor 16 has at least one rotor 32 and, in some embodiments, may
have a plurality of
rotors 32. Each of the rotors 32 are mounted on bearings (not shown).
Alternating current
supplied to windings cause rotor 32 to rotate. Motor 16 may generate heat in a
variety of ways.
For example, friction caused by the rotation of rotor 32 can generate heat or
electrical resistance
in the windings of stator 30 and rotor 32 can generate heat. Indeed, a variety
of electrical and
mechanical components within motor 16 can generate heat. Lubricant within the
motor 16
transfers heat from components of the motor 16 to motor housing 20. Heat is
then transferred
from motor housing 20 to the production fluid on the outside of motor housing
20.
[00051 The rate of heat transfer is determined by the equation Q=h(A)(T);
where Q = rate of heat
transfer, h = the heat transfer coefficient, A = surface area, and T = the
difference in temperature.
The rate of heat transfer between the motor housing 20 and the production
fluid may be
increased by increasing (T), the difference in temperature between the motor
housing and the
production fluid. The difference in temperature may be increased by increasing
the rate of heat
transfer from the heat generating components of the motor 16, such as the
rotor 32 and stator 30,
to motor housing 20.
[00061 Motor 16 uses a lubricant to lubricate the moving parts such as rotor
32 and the bearings
upon which rotor 32 is mounted. The lubricant could be, for example, a
dielectric oil. In
addition to lubricating the parts, the lubricant conducts heat from rotor 32
and stator 30 to the
motor housing 20. Motor 16 may be filled with lubricant, such that lubricant
occupies any
spaces within housing 20. Lubricant pump 34 may be located in the lower end of
housing 20.
Lubricant pump 34 pumps lubricant through motor 16.
[0007) Referring to Figures 2 and 3, in one embodiment, one or more
longitudinal grooves 36
are formed in the ID of motor housing 20 by, for example, stamping or milling
grooves parallel
to the axis of the motor housing 20. Longitudinal grooves 36 are parallel with
the axis of
housing 20. The distance from the recessed surface 38, which is the back of
the grooved portion,
to the axis of housing 20 is greater than the ID of the non-grooved portion
40. Snap ring grooves
42 indicate the location of the ends of the stator 30. The longitudinal
grooves 36 intersect the
circumferential snap ring grooves 42 and extend past the ends of the stator 30
so that oil may
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flow through the groove 36 from one end of the housing 20, past the stator 30
to the other end of
the housing 20.
[0008] In one embodiment, lower reservoir 44 may be a void, filled with
lubricant, located at one
end of motor housing 20. Lubricant pump 34 (Figure 1) may be located within
lower end space
44. Upper reservoir 43 may be a void, filled with lubricant, located at the
other end of motor
housing 20. Reservoirs 44 and 43 are typically located beyond the axial length
of stator 30.
Lower reservoir 44 may be larger or smaller than upper reservoir 43. Some
embodiments may
have just one reservoir 44, or may have other voids, in different locations,
that contain lubricant.
[0009] In one embodiment, longitudinal grooves 36 are in communication with
lower lubricant
reservoir 44 and upper lubricant reservoir 43. The number and spacing of
longitudinal grooves
36 may vary. In the example there are four longitudinal grooves 36 equally
spaced around the
ID of housing 20.
[0010] Grooves 36 increase the surface area of the ID of the motor housing 20.
The increased
surface area increases the rate of heat transfer between the lubricant and the
motor housing 20.
A stator such as stator 30 in Figure 1 closely fits within housing 20. Thus, a
passage is defined
by recessed surface 38, sidewalls 39 of groove 36, and an exterior surface of
stator 30.
[0011] Grooves 36 thus provide a flow channel between stator 30 and housing
20, allowing
lubricant to flow between the stator 30 and the housing, and thus flow in and
out of reservoirs 43,
44. Lubricant pump 34 may cause the lubricant to flow through the passage
associated with
groove 36, thus transferring heat from hotter regions of motor 16 to cooler
regions of motor 16.
For example, heat can be transferred from stator 30 to housing 20.
Furthermore, the lubricant
can be located within the annular gap between stator 30 and housing 20, both
within groove 36
and in the smaller gap outside of groove 36.
[0012] Furthermore, the irregular shape of the grooved ID on the motor housing
20 may create
turbulence within the lubricant. The increased turbulence can increase the
heat transfer
coefficient (h) and thus increase the rate of heat transfer. In an exemplary
embodiment (not
shown), a series of longitudinal grooves is uniformly spaced around the
circumference of the
interior of the motor housing 20, each groove having the same depth, thus
creating a profile that
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is corrugated in appearance. Alternatively, the depths of the grooves or the
depth within a
groove may vary.
[0013] Referring to Figure 4, in another embodiment, circumferential grooves
45 are formed
around the circumference of the ID of the motor housing. The circumferential
grooves 45 follow
a line around the circumference of the motor housing 20, and may be used in
combination with
other grooves such as longitudinal grooves 36. Circumferential grooves 45 may
be located
between the upper and lower ends of the stator so that they are intersected by
longitudinal
grooves 36. The number and spacing of circumferential grooves 45 may vary.
[0014] Referring to Figure 5, in this embodiment helical grooves 46 extend in
helical fashion
around the circumference along the length of the ID of the motor housing 20.
The helical
grooves 46 may be used with longitudinal grooves 36. Furthermore, a single
embodiment could
use grooves running in multiple directions, such that some could be
longitudinal, some could be
circumferential, and some could be at an angle in relation to the axis of the
motor housing 20.
Grooves such as circumferential grooves 45 and helical grooves 46 do not
contain seals or snap
rings; rather they comprise a void filled with lubricant.
[0015] Referring to Figures 6 and 7, an internal groove 50 may also change the
shape of the
outer diameter ("OD") of the motor housing 52. The result would be a raised
surface or rib 54 on
the OD, such that the OD of the raised surface 54 is greater than the OD 56 of
other portions of
the motor housing 52. Like the grooves 36 (Figure 2 and 3), the raised surface
54 may be
longitudinal as shown, circumferential, helical, or a combination thereof. The
raised surfaces 54
can be used to increase the surface area of the exterior of the motor housing
52, increase
turbulence of the production fluid flowing past the housing, or both. The wall
thickness of
housing 52 radially outward from groove 50 may be substantially the same
thickness as between
grooves 50 due to raised surface 54.
[0016] Referring to Figure 8, a stator 60 is a cylindrical component inside
motor housing 20
(Figure 1). The outer diameter of the stator 60 is slightly smaller than the
inner diameter of
motor housing 20. Stator 60 is made up of a large number of thin, flat metal
discs (laminations)
with windings passing through aligned slots in the discs. Stator 60 extends
substantially the
length of the motor housing 20. The stator 60 defines a generally cylindrical
outer diameter and
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central bore. The rotor 32 rotates inside the bore of fixed stator 60,
spinning the motor shaft 14.
In some embodiments, a plurality of rotors 32 rotate inside the bore of stator
60. Each rotor 32 is
made of thin, metal discs also grouped in segments. Longitudinal grooves 64
may be formed in
the OD of the stator 60. The groove or grooves 64 could be generally straight
and extend from
one end of the stator 60 to the other, parallel to the axis of stator 60. The
depth of the grooves 64
may be shallow, such as less than 1/8", or it may be deeper. The width of the
grooves 64 may
vary from less than 1/8" to greater. Stator 60 could be located in a housing
that has a cylindrical
ID free of any oil grooves such as those shown in Figures 2-7. Alternatively,
stator 60 could be
located in one of the housings having grooves, as shown in Figures 2-7. Each
groove 64 defines
a passage bounded on three sides by the three surfaces of groove 64, and on
the fourth side by in
interior surface of housing 20.
[00171 Referring to Figure 9, in this embodiment an internal helical groove 66
could extend
about the cylindrical OD of stator 68 in helical fashion from one end to the
other. Referring to
Figure 10, in this embodiment, the stator stack 70 may have circumferential
grooves 72 on its
OD that are circumferential about the OD of the stator 70 and may promote
lateral lubricant
flow. Any combination of longitudinal, circumferential, and helical grooves
may be used.
[00181 Grooves in the OD of stator stack define passages between the stator
and housing. The
passages promote lateral and linear lubricant movement to transfer heat to the
motor housing
more effectively. The grooves may also increase turbulence in the lubricant,
increase the surface
area that is exposed to the lubricant, and increase the volume of lubricant
between the stator and
the motor housing.
[0019] An ESP motor comprising passages on the ID of the motor housing, OD of
the stator, or
both may be enhanced with other devices that increase the rate of heat
transfer between the
motor housing and the production fluid. A turbulator, for example, can be used
to increase the
turbulence of the wellbore fluid that is in contact with motor 16. Turbulators
are fully described
in U.S. Patent Application 12/416,808, which is incorporated herein by
reference. In one
embodiment, the turbulator, can comprise shroud 80 (Figure 1). Passages on the
ID of housing
and/or the OD of the stator, for example, can increase the heat transfer from
stator 30 to housing
20, and then a turbulator can increase the heat transfer from housing 20 to
the wellbore fluid.
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[00201 Referring to Figure 1, the turbulator, shroud 80, can have an open
lower end 82 and an
upper end sealingly secured around pump 12 above intake 22. The shroud may be
secured by
other means and in other locations. The shroud 80 reduces the cross sectional
area of the path of
fluid flow and thus increases velocity. The higher velocity increases
turbulence, which in turn
increases the heat transfer coefficient (h) of the production fluid flow
across the surface of the
motor housing 20. The shroud 80 may have an irregular sidewall shape 84 to
create pockets of
turbulence between the shroud 80 and the motor housing 20. Furthermore, the
motor housing 20
may have an irregular shape, such as dimples, to promote turbulence in the
wellbore fluid as the
wellbore fluid passes over the exterior of the motor housing.
[00211 Referring to Figure 11, the turbulator comprises multiple dimples 86 on
motor housing 88
of motor 90. The dimples 86 are indentations or protrusions in the exterior
surface of motor
housing 88. The size of the indentations 86 may vary and could be, for
example, made from a
1/4" or 1/2" diameter round punch driven to a 1/8" depth. Dimples 86 could
also have a
significantly larger or smaller diameter and be driven to a greater or lesser
depth. Furthermore,
the dimples 86 may have different shapes such as round, oval, square, and the
like. The dimples
86 may be distributed about the surface in a symmetric pattern or they may be
placed randomly.
The dimples 86 may be concave or convex in relation to the exterior of the
motor housing 88 and
may be used regardless of whether a shroud is used. The dimples 86 increase
the turbulence of
the production fluid and thus increase the rate of heat transfer from the
motor housing 88 to the
production fluid. The dimples give the housing a textured surface. Other kinds
of textured
surfaces may also be used to increase turbulence. The dimples 86 may be used
alone or in
combination with other devices that increase production fluid turbulence.
[00221 Referring to Figure 12, in one embodiment, shroud 92 is a clamshell
configuration,
wherein the shroud can be separated into two or more components. Fins 94 may
be installed on
motor housing 20 (Figure 1) or shroud 92. A fin 94 could, for example, be
welded to the shroud
92 and contact or nearly contact the motor housing 20 when the motor 16 is
installed. This
embodiment overcomes the inherent manufacturing and maintenance difficulties
associated with
attaching fins 94 directly to the motor housing 20, yet still creates
turbulent flow immediately
adjacent to the motor.
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[00231 The fins 94 may be oriented in a variety of positions. In one
embodiment, the fins 94 are
attached at a 90 degree angle or normal in relation to the wall of the shroud
92. Fins 94 may be
slanted in relation to the axis of the shroud 92, such as at a 45 degree
angle. As illustrated by
group 96 of fins 94, adjacent fins 94 may incline at the same inclination
relative to the axis of
shroud 92. Also, some of the adjacent fins 94 may slant at alternating angles
to each other. For
example, one fin 94 is slanted at a 45 degree angle in one direction, and the
adjacent fin is
slanted at an opposing 45 degree angle in the opposite direction, such that
the bottom most edges
98 of the fins 94 are nearest each other and the fins diverge as they go up
along the axis of the
shroud. Other fins 94 may have the same 90 degree opposed orientation, but
with the top most
part 100 of the fins 94 nearest each other. The angle between opposed sets of
fins 98 could be
any angle. The fins 94 may be set at any variety of angles, and the fins need
not be uniform in
layout or in angles. In some embodiments, the fins join shroud 92 at an angle
other than 90
degrees or normal relative to the surface of the shroud.
[00241 The various fin 94 configurations serve to disrupt the laminar flow of
the production fluid
as it flows past the motor housing 20 (Figure 1) and shroud 92. In some
embodiments, the flow
develops swirling or vortexes. The fins 94 may be various lengths, including,
for example, I to 3
inches long. The fins 94 may be attached to the clamshell shroud 92 by, for
example, welding or
adhesives before the halves of the clamshell 92 are joined.
[00251 Other techniques for increasing the rate of heat transfer from motor 16
to the wellbore
fluid may also be used in conjunction with grooves on the ID of housing 20 and
the OD of stator
30. For example, the motor lubricant may be circulated through external oil
tubes. Apparatus
and techniques for external oil circulation are illustrated in U.S. Patent
Application Serial No.
12/632,883, incorporated herein by reference.
[00261 Referring to Figure 12, lubricant may circulate through circulation
tubes 102 located on
the exterior of pump motor 104. Each circulation tube 102 is a passage that is
in fluid
communication with interior portions of motor 104 in at least two locations.
Circulation tubes
102 may attach to oil ports 106, 108 at any point on motor 104. Tubes 102 may,
for example,
attach to oil port 108 at the head of the motor 104, which is the end nearest
the pump, and, for
example, to oil port 106 at the base of motor 104. The circulation tubes 102
may connect to the
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oil ports 106, 108 by a variety of techniques, including, for example, pipe
thread connections,
welding, or quick disconnect fittings, and the like. Lubricant may circulate
by, for example,
entering each tube 102 at port 106, flowing up through tube 102, reentering
motor 102 at port
108, and then passing through the interior of motor 102. When passing through
motor 102, the
lubricant may pass through, for example, grooves 36 located on the ID of
housing 20 (Figure 2)
or grooves 64 on the OD of stator 60 (Figure 8).
[0027] As the lubricant circulates through motor 104 and circulation tubes
102, the lubricant
carries absorbed heat to circulation tubes 102. The exterior surfaces of
circulation tubes 102 are
submerged in and exposed to production fluid inside the wellbore. Thus heat is
transferred from
the circulating lubricant to circulation tubes 102 and then conducted through
the surface of
circulation tubes 102 and transferred to the production fluid. The production
fluid carries the
heat away as it is drawn past tubes 102, into intake 110 of pump 112, and
subsequently pumped
to the surface. Lubricant pump 114 may assist the flow of lubricant through
motor 104 and
circulation tubes 102. The lubricant may flow through circulation tubes 102
from the head
towards the base, or from the base towards the head.
[0028] While the invention has been shown or described in only some of its
forms, it should be
apparent to those skilled in the art that it is not so limited, but is
susceptible to various changes
without departing from the scope of the invention.
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